1. Field of the Invention
The present invention relates to a rotary clamping cylinder actuator having a clamping arm attached to the free end of a piston rod connected to a piston of a hydraulic cylinder actuator and capable of turning the clamping arm between a clamping position in front of a workpiece and an unclamping position apart from the workpiece.
2. Description of the Related Art
A known clamping cylinder actuator shown in FIG. 1 of JP-B-62-5739 has a piston rod provided in its outer surface with a guide groove consisting of a helical guide section extended oblique to the axis thereof and a straight guide section continuous with the helical guide section and corresponding to a clamping angular position, and a guide member, such as a guide pin, connected to an end cover and slidably engaged with the guide groove. When a piston fitted in the cylinder bore of a cylinder and connected to the piston rod is advanced from its back end position, a clamping arm connected to the extremity of the piston rod and positioned at a clamping angular position in front of a workpiece is moved linearly away from the workpiece while the straight guide section of the guide groove moves relative to the guide member. As the piston rod is advanced further, the helical guide section of the guide groove moves relative to the guide member and thereby the clamping arm is turned to an unclamping angular position separated from the workpiece.
The unclamping angular position is determined by the position of the guide member relative to the helical guide section of the guide groove and hence the unclamping angular position is dependent on the stroke of the piston. Therefore, the clamping arm cannot be turned accurately through a predetermined angle and the clamping arm cannot be accurately turned to the unclamping angular position unless the component parts of the clamping cylinder actuator are managed properly to determine the stroke of the piston accurately. When the clamping arm clamping a workpiece is moved from the clamping angular position to the unclamping angular position, the extremity of the helical guide section comes into contact with the guide member and the inertial force of the turning clamping arm exerts intensive shocks on the guide member and the helical guide section of the guide groove, which causes the abrasion of the guide member and a portion of the piston rod corresponding to the extremity of the helical guide section and shortens the life of the clamping cylinder actuator.
When the guide member in engagement with the helical guide section comes into engagement with the straight guide section of the guide groove corresponding to the clamping angular position, the clamping arm, hence the piston rod, stops at the clamping angular position. However, it is not clear whether or not the clamping arm can be stopped accurately at the clamping angular position without exerting intensive shocks on the guide member.
Since the piston rod turns together with the piston, a sealing member (packing ring) fitted around the piston to seal the gap between the piston and the cylinder wall defining the cylinder bore exerts a resistance to the turning of the piston rod. The effect of this resistance is determined by friction between the sealing member and the cylinder wall, and the inside diameter of the cylinder bore. Therefore, the clamping arm cannot be turned unless an axial pressure high enough to turn the piston against the effect of the resistance is applied to the piston.
Accordingly, it is an object of the present invention to provide a rotary clamping cylinder actuator capable of turning a clamping arm through a fixed angle even if the stroke of a piston included therein is not controlled accurately and of reducing the effect of the inertial force of the clamping arm when stopping the clamping arm at an unclamping angular position.
A second object of the present invention is to provide an interlocking mechanism that exerts less resistance to the relative movement of interlocked members than the sliding guide mechanism interlocking a guide groove and a guide pin.
A third object of the present invention is to provide a rod turning mechanism having a rotary rod holding a turning member, such as a clamping arm, and capable of reducing the inertial force of the turning member at the opposite terminal ends of turning motion of the turning member to stop the turning member gradually and of starting turning the turning member at a high turning speed.
A fourth object of the present invention is to provide a rotary clamping cylinder actuator having a rotary member capable of turning under a low resistance and without requiring a high working pressure.
According to the present invention, a rotary clamping cylinder actuator comprises: a cylinder; a piston provided in the cylinder; a front end cover attached to a front end of the cylinder; a rotatable piston rod provided in an outer surface thereof with a guide groove and contained in the cylinder so as to project to outside through the front end cover and capable of rotating about its axis; a guide member attached to one of the cylinder and the piston and engaged in the guide groove of the piston rod so as to be movable relative to the piston rod in directions parallel to the axis of the piston rod; and a clamping arm attached to a free end of the piston rod and capable of being turned together with the piston rod between a clamping angular position and an unclamping angular position; wherein the guide groove has an oblique guide section extending oblique to the axis of the piston rod to turn the piston rod, a first straight guide section connected to one end of the oblique guide section and corresponding to the clamping angular position, and a second straight guide section connected to the other end of the oblique guide section and corresponding to the unclamping angular position, and the oblique guide section and the second straight guide section are so connected that the center of the guide member moves substantially along a circular arc when the guide member moves relative to the piston rod from the oblique guide section to the second straight guide section corresponding to the unclamping angular position.
Since the center of the guide member moves along the circular arc when the guide member moves from the oblique guide section to the second straight guide section corresponding to the unclamping angular position, the guide member is able to move very smoothly relative to the piston rod. Since the piston rod stops after moving straight instead of suddenly stopping while the same is turning, the rotational inertial force of the turning clamping arm can be reduced before the clamping arm stops at the unclamping angular position. Since the angular interval between the two stopping angular positions of the piston rod (hence the clamping arm) is dependent on the angular interval between the first and the second straight guide section, the stroke of the piston does not need to be controlled accurately and the angular interval between the two stopping angular positions can be accurately determined by properly machining the piston rod.
Preferably, the oblique guide section and the second straight guide section corresponding to the unclamping angular position of the guide groove are connected by an arcuate connecting section having the shape of a circular arc, a clamping guide surface of the oblique guide section that engages the guide member when the piston rod is thrust by a piston, and one guide surface of the second straight guide section corresponding to the unclamping angular position are connected by an arcuate connecting surface, and the center of the guide member moves along a circular arc when the guide member is guided by the arcuate connecting surface in the arcuate connecting section.
Preferably, in the arcuate connecting section, an unclamping guide surface of the oblique guide section that engages the guide member when the piston rod is thrust by a piston toward the unclamping angular position, and the other guide surface of the second straight guide section corresponding to the unclamping angular position are connected by an arcuate connecting surface, and the center of the guide member moves along a circular arc when the guide member moves relative to the piston along the arcuate connecting surface.
Since the guide surfaces on the opposite sides of the center line of the arcuate connecting section are arcuate connecting surfaces, the center of the guide member moves along a circular arc when the guide member moves relative to the piston along either of the arcuate connecting surfaces.
Preferably, the guide groove has a semicircular cross section, the guide member is a ball capable of rolling along the guide groove, and the steel ball is supported for rotation in a bearing member.
Since the ball as the guide member rolls along the guide groove, resistance to the movement of the piston rod is relatively low.
Preferably, the piston rod turns between a first angular end position and a second angular end position, the piston rod turns from the first angular end position toward the second angular end position for normal turning and turns from the second angular end position toward the first angular end position for reverse turning, the opposite guide surfaces of the guide groove serve as a first guide surface for normal turning and a second guide surface for reverse turning, respectively, and guide the guide member so that the guide member moves relative to the piston rod along different paths in the guide groove while the piston rod turns for normal turning and reverse turning, respectively, and the first guide surface for normal turning and the second guide surface for reverse turning are formed in shapes that guide the guide member so that the guide member moves relative to the piston along a path inclined to the axis of the piston rod to convert a thrust applied to the piston rod into a torque that turns the piston rod from the first angular end position toward the second angular end position, moves relative to the piston rod along a path having a shape of a section of a sine curve or a cosine curve in a final stage of movement of the piston rod, and moves relative to the piston rod so as not to produce any torque at the second angular end position.
Preferably, the first guide surface for normal turning and the second guide surface for reverse turning are so formed that the guide member moves relative to the piston rod along a path having the shape of a section of a sine curve or a cosine curve.
Preferably, the first and the second guide surface are so formed that a tangent to the sine or the cosine curve at a turning terminating point is parallel to the axis of the piston rod and a tangent to the sine or the cosine curve at a turning starting point is inclined to the axis of the piston rod.
Preferably, the guide groove is so formed that the turning starting point on the path of the guide member for normal turning is separated axially by a distance from the turning terminating point on the path of the guide member for reverse turning, and the turning terminating point on the path of the guide member for normal turning is separated axially by a distance from the turning starting point on the path of the guide member for reverse turning.
Preferably, the piston rod turns between a first angular end position and a second angular end position, the piston rod turns from the first angular end position toward the second angular end position for normal turning and turns from the second angular end position toward the first angular end position for reverse turning, the opposite guide surfaces of the guide groove serve as a first guide surface for normal turning and a second guide surface for reverse turning, respectively, so that the guide member moves relative to the piston rod along different paths in the guide groove while the piston rod turns for normal turning and reverse turning, respectively, and the first guide surface for normal turning and the second guide surface for reverse turning are formed in shapes that guide the guide member so that the guide member moves relative to the piston rod along a path inclined to the axis of the piston rod to convert a thrust applied to the piston rod into a torque at a turning starting point, the guide member moves relative to the piston along a path that decreases gradually the torque produced by the thrust applied to the piston rod and the guide member moves relative to the piston rod so as not to produce any torque at a turning terminating point.
Preferably, in the rotary clamping cylinder actuator in which one end of the cylinder is closed by the front end cover, the piston rod connected to the piston projects to outside from the front end cover and the guide member is combined with the front end cover so as to engage in the guide groove formed in the piston rod so that the piston rod turns when the same is moved axially by the piston, the piston rod is coupled with the piston so as to be turnable relative to the piston.
Preferably, a reduced portion and a shoulder are formed in the piston rod by reducing the diameter of an end portion of the piston rod, the reduced portion of the piston rod is fitted in a center bore formed in the piston, a retaining member for retaining the piston on the reduced portion of the piston rod is attached to the extremity of the reduced portion of the piston rod so that the piston is held between the shoulder of the piston rod and the retaining member with an axial gap between the piston and the shoulder of the piston rod, and the piston rod is turnable relative to the piston.
Preferably, a gap between the reduced portion of the piston rod and a wall defining the center bore of the piston is sealed with a sealing member.
Since the diameter of the connecting portion of the piston rod is smaller than that of the piston, the piston does not turn when the piston rod turns relative to the piston. Since the resistance to the turning of the piston rod is lower than that that acts on the piston rod when the piston turns together with the piston rod. Consequently, the piston rod can be turned by applying a low working pressure to the piston.
Since the guide member is a ball and the ball is supported for rotation in the bearing member, the resistance of the guide member to the turning of the piston rod is low and hence the rotary clamping cylinder actuator can be operated by further reduced working pressure.